Why does lincoln use religious references in his

It is well known that Lincoln grew up in a family that was heavily influentiated by the Baptist church. However, he was very skeptic in his early years. He constantly referred to God and the Bible, and had a deep knowledge of it.

He became even more concerned with religion after two of his children passed away, and attended several Protestant church services with his wife. It's important to note that there is strong evidence that Lincoln didn't believe that Christ was God, but he did believe in a God, creator of all things in the universe.  

This was a strong reason for Lincoln to use a lot of religious and biblical references in his speeches and writings as a president of the US, most particularly during the Civil War.

On July 31, 1846, he stated the following:

"...That I am not a member of any Christian Church, is true; but I have never denied the truth of the Scriptures; and have I spoken with intentional disrespect of religion in general or of any denomination of Christians in particular" -Handbill Replying to Charges of Infidelity.

Hope this helps! Have a great week!